Electrolytic recovery of zinc from zinc-bearing ores and metallurgical products



Sept. 29, 1925. 1,555,567

H. W. GEPP ET Al. f ELECTROLYTIC RECOVERY OF ZINC FROM ZINC BEARING ORESAND METALLURGICAL PRODUCTS Filed July so, 1925 Go SSS P Sheff FurnaceAny excess acid.

purl le V15, 1

Fer-

PumFlcaHon.

Solution Re 'ndues @mnu/bom Mw WMM. W

Lm/'A7 @y W 7% f7@ MW Jaw WMM JM W Patented Sept. 2.9, 1925.

-UNITED `s'm'rlazs- PAT-ENT OFFICE.

y HERBERT WILLIAM GEIP, HARRY HEY, AND GILBERT RIGG, OF MELBOURNE, VIO-TORIA, AND ROYALE HILLMAN STEVENS AND ROWLAND THOMAS DRYLL WIL- LIAMS,OF HOBART, TASMANIA, AUSTRALIA, ASSIGNORS T0 ELECTROLYTIC ZINC COMPANYAUSTRALASIA LIMITED, OF MELBOURNE, VICTORIA, AUSTRALIA. i

ELECTROLYTIC RECOVERY OF ZINC FROM ZINC-BEARING ORES AND METALLURGICAL iPRODUCTS.

Application led July 30, 1923. Serial No. 654,776.

To all whom t may concern:

Be it known that HERBERT WILLIAM GEPP, HARRY HEY, and GILBERT RIGG, all-of Collins House, 360 Collins Street, Melbourne, in the State ofVictoria, ROYALE HILLMAN STEVENS and RowLAND THOMAS DRYLL WIL- LIAMs,both of Risdon, Hobart, in the State of Tasmania, all in theCommonwealth of Australia, have invented certain new and usefulImprovements in the Electrolytic Recovery of Zinc from Zinc-Bearing Oresand Metallurgical Products; and we do hereby declare the following to bea full, clear, and exact description of the invention, such as willenable others skilled in the art to which it appertains to make and usethe same.

This'invention relates to the electrolytic recovery of zinc fromzinc-bearing ores and metallurgical products and refers more especiallyto the recovery of zinc by the electrolytic method from zinc sulphideores (blende), u

This invention is applicable to the treatment of concentrates, tailings,slimes and other metallurgical products, as well as crudev ores, and inthis specification the term ores will include such metallurgicalproducts.

The recovery of zinc by the electrolytic method as at present practised,involves the use of a closed cycle of operations, the roasted ores beingleached with spent electrolyte containin sulphuric acid, the `resultingsolution o? zinc sulphate, after purification, being submitted toelectrolysis for the deposition of cathode zinc'and the formation of anelectrolyte containing sulphuric acid for leaching fresh quantities ofroasted ore.

One known process as at present applied to zinc sulphide ores can bebroadly described as comprising the following steps l, The ore issubjected to a preliminary roasty` for the reduction of the sulphur tofrom 5% to 8%. 2. This partially roasted material is given a finalroastunder such conditions as to control the amount of sulphate sulphurformed and leavingaminimum amount of sulphide sulphur and also for thepurpose of eliminating any chlorine which may be present pulp or residuefrom this last opthen classified in order`- to separate ducing plant,whilst the residues are held f for subsequent treatment.

5. The solution together with the slimes or fine material from theclassifier of step 4 is passed to one or more thickeners, the overflowfrom which passes to the main solution circuit.

6. The thicklened pulp from step 5 is passed to a filter from which theclear solution goes to the .-n `iaiiif-solution circuit The solidresidues from this filtering operation are held for subsequent treatmentas with the residues from the iiotation machine of step 4.

7. The clear solution in the main circuit is passed to a Pachuca tank orother mixing apparatus where an amount of limerock is added toprecipitate and coagulate the iron and silica present.

8. The trate passing to the maln solution circuit, whilst the solids arewithdrawn and discarded. l' r 9. The main solution circuit from step 8is then subjected to purification with -zinc dust for removal of coppercadmium and other impurities. p 10. The purified solution iselectrolyzed with the production of cathode zinc, thus regeneratingsulphuric acid'which is used for leaching as in step 3 in a subsequentcycle.

In the treatment as above described, as at present practised, nosatisfactory method has yet been devised for economically recovering thezinc from the residues mentioned in steps 4 and 6 and making the sameavailable for electro-deposition.

N ow, the object of this invention is to provide certain modificationsin the above cycle of operations whereby a greater proportion of zincfrom a given quantity of ore pulp from step is filtered, the filiresidues and introduced into the main so-v lution'circuit for therecovery ofthezinc by l electrolysis. The gases containing sulphur tionin the dioxide in the presence of which the said heating operation isconducted are passed to an acid plant whereby any excess rsulphuric acidused with the said residues is recovered. This heating -operation iscarried out at a temperature sufficiently high to decompose the ironsulphate formed in the presence' of gas containing SO2 but not highenough to substantially decompose the zinc sulphate.`

This invention as thus summarized comprises the introduction into theelectrolytic method for the recovery of zinc of `a step which comprisesthe treatment of the residues after leaching calcines with spentelectrolyte by mixing the said residues with sulhuric acid, andsubjecting the resultant mixture to a heating or furnacing operaresenceof gases containing sulphur dioxidb (such as roaster gases), andutilizing the gases emanating from such heating or furnacing operationfor the manufacture of sulphuric acid. In the treatment of such residuesin which the zinc -is present mostly as zinc ferrite, we haver foundthat the amount of sulphuric acid required is very little in excess ofthat theoretically necessary for the sulphating of the insoluble zincpresent, and that it is not necessary to add sufiicient sulphuric acidfor thelsulphating of the iron present as well, as any sulphate of ironformed is converted to ferrite oxide in the subsequent operation,liberating SO2 and SO3 which -gases are available for decomposingfurther zinc f errite.

This mixing operation is performed ink such an apparatus as will ensurea complete association of the acid with the material. An apparatussimilar in design to a concrete mixer or a rotating drum has` been foundeffective for the purpose.V

' Incarrying out this mixing operation of the material with acid, .wehave found that nodules can be formed, and the forination of the nodulesfacilitates the subsequent furnacing operation wherein hot roaster gasesare caused t'o pass through the .mixture as in a shaft furnace.

The material with the requisite amount' of acid, which may be added instages, is maintained in a constant state of movement arlxd thereby isagglomerated into the nodu es.

The amount of' permissible moisture will varyaccording to the strengthof acid to be used, and also to the nature of the material. We-havefound when using 98% acid that good nodules can be formed if themoisture content of the residues is approxi-u mately 10%. After themixture has been maintained in a state of movement for some time, anyfines remaining can be agglomerated by the addition of a small amount ofwater. This water forms a plastic massx with the fines and this plasticmass subsequently forms nodules by the movement ory rolling action ofthe apparatus. It has been foundthat the quantity of water added and themanner of its addition has an important bearing on the production of thenodules, but a simple laboratory experiment with any given sample ofmaterial will determine the best conditions. `In some cases it isdesirable that ,weaker acid be used, and with 60% acid We have foundthatfeiicient nodulising can be obtained if both acid and the residuesaforesaid are first heated to a temperature of about 150 C.

This mixture of the zinc-bearing material and sulphuric acid (preferablyin the form of nodules) is then subjected to a heating or furnacingoperation in the presence of gases containing sulphur dioxide or roastergases. l

One form of furnace for this operation is in the nature of ashaftfurnacefwhich may be fed either continuously or intermittently, thesulphur dioxide or Vroaster gases being passed upwards through thecharge of nodules which are of such a' size that a free passage of thegases is permitted. These gases are usually hot, or externall heat maybe applied to maintain the requisite ternperature for the conversion ofall the zinc presentto zinc sulphate. The roaster gases enriched by thissulphating reaction may then be -fpassed toJan acid plant for themanufacture of sulphluric acid. If these gases are to be subsequentlytreated in a contact plant for the recovery of sulphuric acid, it ispreferable that the acidmixed material should be first dried' orA heatedto about 300 C. before roasting with av view 'to the elimination ofmoisture and "noxious gases such as chlorine and luorine.

We do not however confine ourselves to the use of a shaft furnace. Thisfurnacing Q.

type l This furnacing or heating of the ores or other zinc bearingmaterial'mixed with sulphuric acid in the presence of gases con tainingSO2 (such as roaster gases) is carried out preferably at a temperatureabove the dissociation point of the most refractory sulphate of `ironbut below that of the dis sociation point of sulphate of` zinc in thepresence of gases containing SO2. In practice we have found that atemperature of about 670 C. well answers the purpose although goodresults have been -obtained at temperatures ranging from 620- C. to 7 40C.

The sulphate of iron which is formed is converted into ferrie oxide,liberating sulphur dioxide and sulphur trioxide which are available fordecomposition of further zinc ferrite, and at the same time any excesspasses over with roaster gases to the acid plant. In this way,relatively complete con-4 version of the zinc to sulphate is effected,whilst any excess acid added over that consumed in the sulphating of thezinc is substantially recovered, the iron being left for the most partin insoluble form. The insoluble zinc compounds are thus converted tosoluble zinc sulphate, and may be leached outand used for the recoveryof zinc by the electrolytic methodor for the manufacture of lithloponeor for any other industrial purpose.

In adapting this invention to the known' methods for the electrolyticrecovery of zinc from zinc sulphide ores (blende) such as 'representedby the aforesaid cycle of operations or sequence of steps severalmodlfications may be adopted. Upon the accompanying sheet of drawings isillustrated a flow sheet of one such modification.

The zinc bearing ores as at A, usually in the form of concentrates, areroasted as at B so as to contain about 5% sulphur as sul hide. Thisroasted ore is then leached at with spent electrolyte lcontaining'sulphuric acid. The pulp from C passes a classifier D which delivers aproduct of slimes on the one hand relatively low in sulphide Ysulphurand a coarse material,

on the other hand relatively high in sulphide sulphur. l

A The slimes from the classifier D pass to thickeners E, whilst thecoarse material from D passes to flotation machines F. The overflow fromthe thickeners E passes to an agitator G where it is treated withlimerock and is then filtered as at H, the clear solution passing to themain solution circuit for purication and thence to the electrolyticcells,1 whilst the solids are dumped. The pulp or residue from thethickeners-E passesto filters J, the clear solution from which joins theoverflow from the thickeners 15, whilst the solids pass to a dryer K.The productsfrom the dotation machines F consist of tail ings on the onehand relatively low in sulhide sulphur and concentrates on the otherliand high in sulphide sulphur. The tailthe solids from the filters ingsfrom the flotation machines F pass to filters L, the solids fromwhichjoin s J n The concentrates from the lflotation machines F `pass toroasters M, the gases from which are utilized as hereinbefore described,while the calcines are returned to the leaching tanks at C. The materialpassing to the dryers K from the filters J and L is. mixed with aabout30% of its dry weight of sulphuric acid (98%) and maintained'in aconstant state of movement in a suitable machine, such as a concretemixing machine N, whereby it is formed into nodules. The amount of acidrequired will depend upon the yamount of insoluble zinc present in thematerial.

The nodulized material from N is then dried, as at O, and delivered intoa shaft furnace P at vthe same 'time the roaster gases from Mpassupwards through the nodules in the shaft furnace ,P, so that thesaid nodules are subjected to a lheating or furnacing operation at atemperature of approximately 670 C. The treated material from the shaftfurnace P, now being low in sulphuras sulphide but the zinc content ofwhich has been converted to zinc sulphate, is delivered to leachingtanks R where it is leached, with main circuit solution. The Vgases fromthe shaft furnace P, after suitable scrubbing, are passed to an acidplant T, thereby supplying a portion `of the acid necessary for themixing with the material at B. The pulp from R is delivered to ,settlersW, the clear solution from which passes to the main circuit and the pulpfromwhich goes to agitators X where it is treated with limerock, afterwhich it is filtered at Y the clear liquor from which goes to the mainsolution circuit Whilst the residue is dumped for further treatment.A

be seen that the second or final roasting of step 2 as ordinarilypracticed has been omitted, and that theV ore is leached with spentelectrolyte only after the partial roasting of step 1. Owing-tothis'roasting having been only partial there will'be more materialpassing to the flotation machines than heretofore and consequently agreater'quantity of flotation concentrates containing sulphides. Thesefiotation concentraties. are roasted, the gases' therefrom being usedand the residues therefrom being treated as hereinafter described, Inlthe furnacinig operation ofthe residues mixed with sulphuric acid, acertain amount of silver is rendered 'soluble and this silver. isprecipitated by chlorides contained in the leaching By Vmodifying thepresent treatment as are pres-` purpose, soluble4 chlorides willl vabove set out, it will be seen that it is not necessary to' aim at amaximum conversion of zinc sulphide to zinc sulphate in the origithatrequired for the sulphating of the residues can be utilized for otherindustrial purposes. u l

However, this; modified treatment of th invention is not confined to thepartial roasted product of step (l) but may be also applied to thefinally roasted product of step (2) butin such case the flotationconcentrates (from step 4) would be less in quantit'y but any deficitmay be made up by additions of untreated ore, should there be in-Isuflicient for the product-ion of the necessary amount of roastergases, or such roaster gases may be those resulting from the finalroasting of the untreated ore (as in step 2) as above described.Similarly, the treatment is applicable to material which has been deadroasted.

In some cases it may be desirable to carry out the heating operation ofthe mixture of residues and sulphuric acid other than in the presence ofroaster gases; for example, the said heating operation may be effectedin a muile or other suitable furnace and the SO2 and SO3 recoveredtherefrom by appropriate means, if desired.

lVe claim 1. The process of electrolytic recovery of zinc fromzinc-bearing material which consist-s in roasting the zinc-bearingmaterial, leaching the roasted material with an acid solution,separating the solution from the residues, mixing the residues withsulphuric acid, furnacing the resulting mixture in the presence ofsulphur dioxide to-renderl the contained zinc soluble, and recovering byelectrolysis the zinc which has been rendered soluble.

2. The process of electrolytic recovery of Zinc from zinc-bearingmaterial which consists in roasting the zinc-bearing material, leachingthe roasted material With an acid solution, separating the solution fromthe residues, mixing the residues with sulphuric acid, furnacing theresulting mixture in the presence of sulphur dioxide to' render thecontained zinc soluble, treating the resulting gases for the productionof sulphuric acid therefrom, and recovering by electrolysis the zincwhich has been rendered solusists in leaching the zinc-bearing materialvturein the presence of sulphur dioxide tom render the contained zincsoluble, leaching fthe furnaced product to obtain a vsolution containingthe soluble zinc, and recovering the zinc from the solutions byelectrolysis.

5. The process of electrolytic recovery of zinc from zinc-bearingmaterial which consists in leaching the material With an acid solutionto yield a main circuit zinc-bearing solution and residues, `separatingthe residues, mixing the lresidues with sulphuric acid, heating theresulting mixture in the presence of gases containing sulphur dioxide torender the zinc soluble, leaching the heated product to extractthesolublezinc and produce a zinc-bearing solution, recovering the zincfrom the solutions by electrolysis, and treating said sulphur dioxidegases to produce sulphuric acid therefrom.

6. The process of electrolytic recovery of zinc from zinc-bearingmaterial which-consists in roasting the zinc-bearing material, leachingthe roasted material with an acid solution to form a main circuitsolution,

roasted material with an acid solution to produce a zinc-bearing maincircuit solution, separating the residues, mixing the re sidues withsulphuric acid so as to form nodules and heating the nodules in roastergases from said roasting operation to render the zinc soluble, treatingthe resulting gases to produce sulphuric acid, leaching the heatedproduct to `Aobtain a solution containing the soluble zinc, andrecovering the zinc from the solutions by electrolysis. l

8. The process of electrolytic recovery of zinc from zinc-bearingmaterial containing sulphides which consists in roasting the material toconvert part of the sulphides to oxides and produce calcines, leachingthe calcines With acid-bearing spent electrolyte, separating theresulting zinc-bearing solution as a main circuit solution, subjectingthe residues to froth-flotation separation to produce concentrates andresidues, roasting the concentrates, adding Jthe roasted concentrates tothe calcines, mixing the iotation residues with sulphuric acid andheating in the presence of roaster gases from a previous step, leachingthe heated residues to obtain a solution containing the soluble zinc,recovering the zinc :from the solutions by electrolysis, and treatingthe gases from the heating operation to produce sulphuric acid.

9. The process of electrolytic recovery of zinc from Zinc-bearingmaterial containing sulphides Which consists in roasting the ores toconvert part of the sulphides to oxides as calcines, leaching thecalcines with acidbearing spent electrolyte to produce a main circuitsolution, separating the coarse material from the fines and from thesolution,

subjecting the coarse material to froth-flotation separation, roastingthe resulting concentrates to produce calcines, mixing the leached finesand the residues from frothlotation with sulphuric acid, heating thesulphuric-acid-treated material lin the presence of roaster gases fromthe roasting of the calcines, treating the resulting gases to producesulphuric acid therefrom, leaching the sulphuric-acid-treated product toobtain a solution containing the soluble zinc, and recovering the zincby electrolysis from the solutions.

In testimony that We claim the foregoing as our invention We have signedour names to this specication.

HERBERT WILLIAM GEPP.

HARRY HEY. GILBERT RIGG. ROYALE HILLMAN STEVENS. ROWLAND `THOIIIS DRYLLWILLIAMS.

